As is known in the art, the process of image reconstruction includes several processes of rebuilding an image from a number of different image projections, the image projections being obtained, e.g., using computed tomography angiograms or other imaging modalities. Four-dimensional (4D) reconstruction involves the reconstruction of a 3D image as a function of a fourth parameter, e.g. time, the resulting 4D reconstruction permitting, e.g., the user to understand how the reconstructed 3D image behaves over time. The 4D reconstruction can serve as the basis for a prediction model, whereby information is provided as to behavior of the image over time. 4D reconstructions have been implemented in the field of medical imaging to visualize and model aneurysms in arteries of the human body, e.g., “CT Angiography with Electrocardiographically Gated Reconstruction for Visualizing Pulsation of Intercranial Aneurysms: Identification of Aneurysmal Protuberance Presumably Associated with Wall Thinning,” M. Hayakawa et al., Am J Neroradiol, vol. 26, pgs. 1366-1369, June/July 2005, and Prediction of Impending Rupture in Aneurysms Using 4D-CTA: Histopathological Verification of a Real-Time Minimally Invasive Tool in Unruptured Aneurysms.” Y. Kato et al. Minim. Invas. Neurosurg. Vol 47, pgs 131-35, 2004.
Techniques to obtain a 4D reconstruction have been disclosed by U.S. Pat. No. 6,643,392. This reference describes a technique whereby 2-D projections of an image are obtained at specific time intervals (or cardiac phases) over multiple cycles of periodic motion, each group of 2-D projections obtained at a particular cardiac phase serving as the basis for building a corresponding 3D reconstruction. Multiple 3D reconstructions are subsequently built, each 3D reconstruction corresponding to a particular time interval or cardiac phase.
Subsequently, two successive 3D reconstructions are used to derive a law of geometric/spatial deformation occurring therebetween, this process repeated for each pair of successive 3D reconstructions. Finally, each of the 2-D projections is applied to the derived laws of spatial deformation to arrive at the 4D reconstruction of the image.
The processes by which the 4D reconstruction is built suffer from some disadvantages, one being the large number of 2-D projections required for accurate rending of the 4D reconstruction. For example, it is expected that two hundred or more 2-D projections would be needed to accurately build each of the 3D reconstructions, and twenty or more 3D reconstructions are needed to derive an accurate 4D reconstruction, resulting in approximately four thousand 2-D projections needed. Furthermore, if image artifacts are present in one of the pair of 3D reconstructions used to derive the spatial deformation law, the 3D-3D registration process used to derive the spatial deformation laws could operate to map those artifacts into two of the spatial deformation laws (as the 3D reconstructions other than the beginning and end 3D reconstructions are used twice), resulting in the errors being transferred to the resulting 4D reconstruction. When the above mentioned method is used with fewer projections, e.g. ten projections per motion phase with a total of twenty phases, it is very likely that during the 3D-3D registration process artifacts would be mapped to define the spatial transformation instead of anatomical structures.
Accordingly, what is needed is an improved 4D reconstruction process requiring fewer 2-D projections and which provides less artifact transmission.